The present invention relates to an antenna with a transmission part and a receiving part separated from each other; and, more particularly, to a Radio Frequency Identification (RFID) reader antenna whose transmission ports and reception ports are highly isolated from each other by using a quadrature hybrid coupler.
Radio Frequency Identification (RFID) readers are used in diverse fields, such as material management and security, along with an RFID tag, or transponder. Generally, when an object with an RFID tag attached thereto is disposed in a read zone of the RFID reader, the RFID reader modulates an RF signal which has a predetermined carrier frequency and sends an interrogation to the RFID tag. Then, the RFID tag responds to the interrogation from the RFID reader.
In short, the RFID reader transmits an interrogating signal to the RFID tag by modulating a continuous electromagnetic wave, which has a predetermined frequency. Then, the RFID tag performs back-scattering modulation onto the electromagnetic wave transmitted from the RFID reader to return its own information stored in a memory inside the RFID tag.
Back-scattering modulation is to modulate the intensity or phase of a scattered electromagnetic wave when an RFID tag returns an electromagnetic wave outputted from an RFID reader after scattering. Herein, since the RFID tag simply performs the back-scattering modulation onto the electromagnetic wave transmitted from the RFID reader, the carrier frequency of the electromagnetic wave transmitted from the RFID to the RFID reader is the same as the carrier frequency of the electromagnetic wave transmitted from the RFID reader to the RFID tag.
An RF receiver of the RFID reader receives not only signals transmitted from the RFID tag, but also some transmission signals transmitted from an RF transmitter of the RFID reader due to leakage. Herein, since the two kinds of signals have the same carrier frequency, the RF receiver of the RFID reader cannot separate one from the other even with a filter.
Generally, the intensity of the transmission signals leaked out of the RF transmitter of the RFID reader is higher than that of the signals transmitted from the RFID tag. The leakage signals degrade the reception sensitivity of the RFID reader.
To reduce leakage power from the RFID transmitter of the RFID reader, suggested is a method of forming two radiating bodies, i.e., a transmission part and a reception part, respectively, in an RFID reader antenna, and disposing them apart from each other with wide space between them to thereby isolate the transmitting port and the receiving port from each other. The method, however, has a problem that the antenna becomes large due to the wide space between the two radiating bodies.